I hope I will be able to hunt with the upper 47-51 pound (at my draw length of 26") for as long as I'm able to hunt.
However, if I am someday unable to hunt with those weights I'd feel comfortable, with proper game angle, perfectly tuned arrow, and razor-share broadhead, effective at 40 pounds.
I've killed many white-tail, mulies, antelope, and black bear over the years with Bear Razorheads. I started shooting single-bevel Helix broadheads in 2010. I'm not suggesting they are better than double bevel but I am very pleased with the Helix. I have a half-dozen unshot Silver Flames in my broadhead drawer. I'm sure they would work just fine but I have no reason to change.
Five for five on boiler room shots the past 3 years. Not a single deer has gone further than 35 yards after the hit.